The invention relates to a method for preparing a biological glue capable of coagulating simply by addition of calcium ions.
It is known that protein concentrates containing fibrinogen and factor XIII in particular can coagulate by adding thrombin to produce a fibrin network, and are used as adhesives. More specifically, under the effect of the thrombin, the fibrinogen is converted into fibrin monomer. The fibrin monomers assemble into fibrin polymers. Under the action of factor XIII activated by thrombin, in the presence of calcium ions, the fibrin chains are crosslinked. Thus, the addition of thrombin, followed by application of the resulting mixture, causes coagulation by formation of fibrin on the parts to be glued, by a mechanism that mimics the end phase of blood coagulation. Thus, by coagulating, the fibrinogen concentrates constitute a glue that can join living tissue and keep it joined while producing a hemostatic action; see for example patent FR-2448900. Such glues are commonly called "biological glues" or "fibrin glues" and are used in surgery, particular to prevent or stop bleeding, replace or reinforce suture threads, hold grafts in place, for example skin grafts, bring together tissues that have undergone resection, for example in lung or gastrointestinal tract surgery, or to glue parts of prostheses, etc.
When biological glues are used, thrombin should be available, prepared from human or animal blood plasma mixtures. Homologous products, i.e. products of human origin for which the donor and recipient are different, carry the risk of contaminating the recipient by pathogens from the donor. This risk can be reduced by donor selection and screening for pathogen markers in the donor, or physical/chemical treatments that destroy the prepared products or diminish their virulence. However, there can be no certainty that homologous products are safe.
Products prepared from animal tissues also carry risks linked to the existence of pathogens transmissible to humans, and also risks of immunization and hence anaphylactic reactions.
The above risks would be avoided if solely autologous products, i.e. products prepared only from material taken from the future recipient, were used.
The principle of autologous transfusion is known and extremely widespread, as is the preparation of fibrinogen-based glues. However, the so-called "autologous" glues are only truly autologous as far as the fibrinogen solution is concerned. In fact, the thrombin solution is obtained from homologous or heterologous plasmas, but not autologously; see in particular Cederholm-Williams, Lancet 344, 336-337 (1994).
Patent Application PCT WO94/07548 describes a biological glue enriched with platelet factors that is able to coagulate without addition of thrombin by adding, to the recalcified glue, an activator of the blood coagulation contact phase such as kaolin. However, in this patent application, the contact phase activator is incorporated at the time the glue is used, which makes activation uncertain and difficult because the fibrinogen concentrate is a highly viscous product, difficult to handle. As a result, coagulation time is difficult to control. Moreover, since coagulation progresses along with activation, it is difficult to separate the activator from the activated glue.